1. Field of the invention
The present invention relates to attachment devices which mount in an opening formed in a wall and which may be mounted in this opening from one side only. It relates in particular to the attachment of various apparatus, such as lamps, switches and contacts with, where appropriate, a manual control for the apparatus on the other side of the wall.
2. Description of the prior art
There are already known attachment devices of this kind comprising:
a body equipped with a cylindrical head designed to be inserted and locked into an opening in a wall,
locking means comprising retractable claws disposed around the perimeter of and in the vicinity of the end of the cylindrical head and which, when the cylindrical head is inserted into the opening, retract in line with the edges of the latter and then move apart so as to prevent withdrawal of the cylindrical head from the opening, and
clamping means disposed in the vicinity of the base of the cylindrical head which cooperate with the locking means to immobilize the cylindrical head in the opening in the longitudinal direction by exerting on the wall forces opposing those exerted by the locking means.
In one known embodiment, the clamping means consist of a ring designed to bear against the wall, fitted to the head below said claws and to the base of the body and urged against the wall by a set of compression springs trapped between the ring and the base of the body.
Devices of this kind, in this embodiment, require of the operator, when they are fitted into the opening in the wall, the deployment of a force sufficient to hold the springs highly compressed, which permits the ring to move away from said claws and likewise the elastic retraction of the latter in line with the edges of the opening, during the proper positioning of the head in the opening. These devices also have the disadvantage of allowing axial displacement within the opening, after they are fitted into it, through compression of the springs, during the fitting of the apparatus which they accommodate, for example, or during work on the apparatus, and capable of leading to the detachment of the control or indicator members mounted on the device in front of the wall.
The object of the present invention is an attachment device which is extremely simple to fit into an opening in a wall and with which all possibility of axial movement after fitting to the wall is eliminated.